zerodds-spy

Subscribe to a DDS topic and dump samples — like tcpdump for DDS.

The tool starts a DcpsRuntime and type-follows the topic: it discovers each writer's real IDL type via SEDP and attaches one opaque reader per type (so it sees typed topics like cuas::Track, not just zerodds::RawBytes). It prints metadata + an optional hex snippet of every incoming sample until you Ctrl-C, hit a sample-count limit, or a duration elapses. Late-joining writers (and additional types on the same topic) are picked up automatically.

Pass --type <NAME> to announce a type directly and skip discovery — useful for a writer that is silent or joins after the spy.

Usage

# Subscribe to topic Foo on default domain (0) until Ctrl-C
zerodds-spy -t Foo

# Capture exactly 50 samples
zerodds-spy -t Foo -n 50

# 10s burst, dump only first 8 hex bytes per sample
zerodds-spy -t Foo --duration 10s --hex 8

# Subscribe on domain 5
zerodds-spy -d 5 -t Sensor/Stream/A

Decoded output (--decode)

With --decode --type-file <IDL>, each sample is decoded against its writer's IDL type and printed as compact JSON instead of hex. Types resolve lazily per discovered writer type and are cached; a sample whose type isn't in the IDL (or that doesn't decode) falls back to the hex line.

zerodds-spy -t TrackTopic --decode --type-file tracks.idl
# [     1] writer=000003c2 type=cuas::Track {"id":42,"name":"bandit","xs":[7,-3,1000]}

Output

Each sample is printed as one line:

[     1] writer=000003c2 bytes=64 deadbeef cafebabe 12345678 90abcdef
[     2] writer=000003c2 bytes=64 deadbeef cafebabe 12345678 90abcdef
...

Lifecycle markers (Disposed / Unregistered) are printed as [lifecycle] <kind>.

Exit Codes